Hydraulic spring energy store drives for actuating high-voltage circuit breakers are known, for example, from DE 3408909 A1 and EP 0829892 A1 and can include, inter alia, a storage module for actuating a high-voltage switch including a spring element acting as an energy store. The spring element interacts with a movable storage piston guided in a hydraulic block. The storage module is intended for providing pressure energy to the hydraulic drive of the high-voltage circuit breaker without any further supply of external energy and for actuating the drive and, thereby, the circuit breaker correctly, even in the event of a fault or an interruption to the energy supply.
The state of stress of the spring element can be monitored constantly via a spring excursion switch. Owing to the reloading of the hydraulic pump integrated in the spring energy store drive which sometimes occurs in order to compensate for low internal pressure losses in the hydraulic system of the spring energy store drive, even without any preceding switching operation, permanent self-monitoring of the drive function of the spring energy store drive can be ensured even in the case of long standstill times.
EP 2 313 901 B1 describes a spring energy store drive whose spring element, also referred to below as storage spring, pressurizes a fluid, for example oil, located in the storage cylinder via a pressure body and a pressure piston which is movable in sliding fashion in a storage cylinder. A drive rod which is fastened on a drive piston, which is movable in sliding fashion in a working cylinder, is moved by this fluid.
During a switching operation, a certain quantity of oil is removed from the storage module and thus the spring element is relieved of tension. In order to determine the loading state of the spring energy store drive, a spring excursion switch can be used, which is mechanically connected to the spring element. If the drive or working piston moves with the drive or working rod into a first end position, it closes the circuit breaker. If the working piston is moved with the working rod into a second end position, it opens the circuit breaker.
Depending on the spring stress of the spring element, bistable actuating or contact elements are actuated via a gear mechanism arrangement, which actuating or contact elements are intended, for example, to inhibit switching operations when insufficient switching energy is stored in the spring element, for example owing to internal leakage losses in the hydraulic system of the spring energy store drive.
One of the provided contact elements serves the purpose of controlling the motor of the spring energy store drive for reloading of the storage module. If the spring excursion of the storage module in the form of a spring element falls below a preset value, the motor is switched on and tensions the spring element up to a switch-off point which is above this value. The difference between the switch-off point and the switch-on point of the motor is also referred to as reloading hysteresis and results from hysteresis in the switching operation of the bistable contact elements.
The spring excursion switches used in known hydraulic spring energy store drives use the hysteresis of the switching contacts themselves to achieve reloading hysteresis. As is shown in FIG. 1, the switching contacts are moved, for this purpose, by an actuating element 20 with a cam, referred to below as actuating cam 21, wherein the cam can have a two-step configuration for this purpose.
Owing to the two-step configuration of the actuating cam 21, the switching hysteresis of the spring excursion switch is adjustable by virtue of an actuating or contact lever 11 of a switching element 10 of the spring excursion switch, which actuating or contact lever is guided via the actuating cam 21, remaining for a stroke 23 of the actuating cam 21 which is to be defined precisely in a position 22, which is between the switch-on and switch-off points of the switching element. This arrangement can only be used when the switching hysteresis of the switching element used, i.e. the differential distance between the switch-on and switch-off points, is sufficiently great. For example when small and therefore generally inexpensive switching elements are used, this switching hysteresis is generally extremely small. An increase in the hysteresis of the entire system can often only be implemented technically with a large amount of complexity, or not at all, when using a two-step actuating cam.